The present invention relates to an optical scanner configured to scan a photosensitive member with a light beam to form an electrostatic latent image on the photosensitive member.
Generally, an optical scanner used for a laser printer has various optical elements, such as a semiconductor laser, a coupling lens, a reflecting mirror, and a cylindrical lens which constitute an incident optical system, and a deflecting mirror, a scanning lens, and a reflecting mirror which constitute a scanning optical system. Of these optical elements, a lens produces stray light when a light beam is reflected on its incidence surface and emission surface. If the stray light reaches a photosensitive member, a ghost image may be formed, thereby leading to deteriorated image quality. Particularly, in the case where stray light occurs in the incident optical system and reaches the photosensitive member, only little stray light becomes a problem because the optical path of the stray light beam is unchanged and the photosensitive member is continuously irradiated with the stray light at the same area.
To eliminate this problem, for example, Japanese Laid-open Patent Publication No. 2003-195209 discloses an image exposure device including a limiter such as a light filter and a half mirror on an optical path of light beam emitted from a laser beam source (semiconductor laser) that emits a large amount of stray light. Because the limiter limits the amount of light emitted from the laser beam source to the required amount for exposure, this image exposure device can restrict stray light from the laser beam source.
However, in this conventional image exposure device, a laser beam from the laser beam source goes around the limiter and can be incident on the reflecting mirror and the cylindrical lens that is arranged on an optical path adjacent thereto. This conventional image exposure device is therefore insufficient to restrict stray light generated in the incident optical system from reaching the photosensitive member. Further, this image exposure device is much less sufficient to restrict stray light caused by a laser beam from another laser beam source.
In view of the foregoing drawbacks of the prior art, the present invention seeks to provide an optical scanner which can sufficiently restrict stray light generated in an incident optical system from reaching a photosensitive member.